A magnetoresistance element such as a giant magnetoresistance (GMR) element, a magnetic tunnel junction (TMR) element, or an anisotropic magnetoresistance (AMR) is often used as a magnetic sensor (see Published Japanese Translation No. 2005-513475 of the PCT International Publication). The magnetoresistance element is an element whose output resistance value changes depending on an input magnetic field. The change in the detected magnetic field can be measured according to the output resistance value.
FIGS. 7 and 8 are diagrams showing a conventional biosensor 500. As shown in FIG. 7, the biosensor 500 includes a substrate 101, a magnetoresistance element 102, a protective film 107, and a biomolecule capture layer 109 for capturing target biomolecules in this order. In the case where biomolecules in a sample are captured by the biomolecule capture layer 109, magnetic beads having an affinity for the biomolecules are captured on the biomolecule capture layer 109 through the biomolecules, and then a magnetic field is horizontally applied (applied magnetic field 105), a stray magnetic field 111 is generated from magnetic beads 104, and the stray magnetic field 111 is input to a magnetoresistance element 102.
FIG. 8 is a diagram showing the details of a conventional magnetoresistance element 102 used in a conventional biosensor 500. As shown in FIG. 8, the magnetoresistance element 102 has a set of three meander structures.
As shown in FIG. 7, in the conventional biosensor 500, since the application direction of the external magnetic field coincides with the magnetosensitive direction of the magnetoresistance element 102, in the case where the applied magnetic field 105 as an external magnetic field is strengthened in order to increase the stray magnetic field 111 from the magnetic beads 104, there has been a problem that the magnetization of the magnetosensitive layer of the magnetoresistance element is saturated and therefore the required output could not be obtained.
As shown in FIG. 8, in the case of the meander structure, there are a case where the magnetic beads 104 are disposed on the magnetoresistance elements 102 and a case where the magnetic beads 104 are disposed between the magnetoresistance elements 102. Since the output changes due to differences in placement, that is, due to the relative position of the magnetoresistance elements 102 and the magnetic beads 104, there has been a problem that sufficient accuracy could not be obtained because of variations in the measurement value of the quantity or concentration of the magnetic beads.